Shaped abrasive particles with a sloping sidewall

ABSTRACT

Shaped abrasive particles each having a sloping sidewall, each of the shaped abrasive particles comprising alpha alumina and having a first face and a second face separated by a thickness, t. The shaped abrasive particles further comprising either: a draft angle α between the second face and the sloping sidewall, and the draft angle α is between about 95 degrees to about 130 degrees, or the sloping sidewall having a radius, R, between the first face and the second face and the radius, R, is between about 0.5 to about 2 times the thickness, t.

BACKGROUND

Abrasive particles and abrasive articles made from the abrasiveparticles are useful for abrading, finishing, or grinding a wide varietyof materials and surfaces in the manufacturing of goods. As such, therecontinues to be a need for improving the cost, performance, or life ofthe abrasive particle and/or the abrasive article.

Triangular shaped abrasive particles and abrasive articles using thetriangular shaped abrasive particles are disclosed in U.S. Pat. Nos.5,201,916 to Berg; 5,366,523 to Rowenhorst; and 5,984,988 to Berg. Inone embodiment, the abrasive particles' shape comprised an equilateraltriangle. Triangular shaped abrasive particles are useful inmanufacturing abrasive articles having enhanced cut rates.

SUMMARY

Shaped abrasive particles, in general, can have superior performanceover randomly crushed abrasive particles. By controlling the shape ofthe abrasive particle it is possible to control the resultingperformance of the abrasive article. The inventors have discovered thatby making the shaped abrasive particle with a sloping sidewall having adraft angle between about 95 degrees to about 130 degrees severalunexpected benefits occur.

First, the shaped abrasive particles with the sloping sidewall tend torest on the make coat of a coated abrasive article at an anglecorresponding to the draft angle of the sidewall. It is believed that adraft angle other than 90 degrees results in the shaped abrasiveparticles leaning instead of having a 90 degree orientation to thebacking in a coated abrasive article since the sidewall, which theshaped abrasive particle in the coated abrasive rests on, is sloped dueto the draft angle. Because the shaped abrasive particles are mostlytipped or leaning to one side due to the angled sidewall they rest on,they can have an orientation angle less than 90 degrees relative to thebacking thereby enhancing cut rates.

Secondly, the shaped abrasive particles with the sloping sidewall canhave different draft angles for different sides of the shaped abrasiveparticle. For example, an equilateral triangle can have a first sidewallat a first draft angle, a second sidewall at a second draft angle, and athird sidewall at a third draft angle, wherein the first, second, andthird draft angles are different. A resulting coated abrasive articlemade from the shaped abrasive particles with the three differentsidewall angles will tend to have an even distribution of particleslanding on each of the three sidewalls. As such, the coated abrasivearticle will tend to have three distinct heights for the tips of theshaped abrasive particles from the backing. The sidewall contacting themake coat with the largest draft angle will have the lowest tip height,the sidewall with the intermediate draft angle will have an intermediatetip height, and the sidewall with the smallest draft angle will have thehighest tip height. As a result, the coated abrasive article willpossess shaped abrasive particles having three distinct orientationangles relative to the backing and three distinct tip heights. It isbelieved that such a coated abrasive article will possess more uniformcutting performance as the abrasive article wears due to the unusedshorter tips of the shaped abrasive particles coming into contact withthe workpiece as the taller tips of the shaped abrasive particles tendto wear down.

Hence, in one embodiment, the disclosure resides abrasive particlescomprising shaped abrasive particles each having a sloping sidewall,each of the shaped abrasive particles comprising alpha alumina andhaving a first face and a second face separated by a thickness, t. Theshaped abrasive particles further comprising either: a draft angle αbetween the second face and the sloping sidewall, and the draft angle αis between about 95 degrees to about 130 degrees, or the slopingsidewall having a radius, R, between the first face and the second faceand the radius, R, is between about 0.5 to about 2 times the thickness,t.

BRIEF DESCRIPTION OF THE DRAWING

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentdisclosure, which broader aspects are embodied in the exemplaryconstruction.

FIG. 1A illustrates a top view of one embodiment of a shaped abrasiveparticle.

FIG. 1B illustrates a side view the shaped abrasive particle of FIG. 1A.

FIG. 1C illustrates a side view of coated abrasive article made from theshaped abrasive particles of FIG. 1A.

FIG. 2 illustrates a photomicrograph of the shaped abrasive particles.

FIG. 3 illustrates a photomicrograph of the top surface of a coatedabrasive article made from the shaped abrasive particles of FIG. 2.

FIG. 4A illustrates a top view of another embodiment of a shapedabrasive particle.

FIG. 4B illustrates a side view the shaped abrasive particle of FIG. 4A.

FIG. 4C illustrates a side view of coated abrasive article made from theshaped abrasive particles of FIG. 4A.

FIG. 5A illustrates a top view of another embodiment of a shapedabrasive particle.

FIG. 5B illustrates a side view the shaped abrasive particle of FIG. 5A.

FIG. 5C illustrates a side view of coated abrasive article made from theshaped abrasive particles of FIG. 5A.

FIG. 6 illustrates a graph of Cut Rate versus Time for shaped abrasiveparticles with different draft angles.

FIG. 7 illustrates a graph of Total Cut versus Time for shaped abrasiveparticles with different draft angles.

FIG. 8 illustrates a photomicrograph of prior art abrasive particlesmade according to U.S. Pat. No. 5,366,523.

FIG. 9 illustrates a photomicrograph of a cross section of the prior artabrasive particles of FIG. 8.

FIG. 10 illustrates a photomicrograph of a cross section of the priorart abrasive particles of FIG. 8.

FIG. 11 illustrates a photomicrograph of a cross section of a shapedabrasive particle with a sloping sidewall.

Repeated use of reference characters in the specification and drawingsis intended to represent the same or analogous features or elements ofthe disclosure.

DEFINITIONS

As used herein, forms of the words “comprise”, “have”, and “include” arelegally equivalent and open-ended. Therefore, additional non-recitedelements, functions, steps or limitations may be present in addition tothe recited elements, functions, steps, or limitations.

As used herein, the term “abrasive dispersion” means an alpha aluminaprecursor that can be converted into alpha alumina that is introducedinto a mold cavity. The composition is referred to as an abrasivedispersion until sufficient volatile components are removed to bringsolidification of the abrasive dispersion.

As used herein, the term “precursor shaped abrasive particle” means theunsintered particle produced by removing a sufficient amount of thevolatile component from the abrasive dispersion, when it is in the moldcavity, to form a solidified body that can be removed from the moldcavity and substantially retain its molded shape in subsequentprocessing operations.

As used herein, the term “shaped abrasive particle”, means a ceramicabrasive particle with at least a portion of the abrasive particlehaving a predetermined shape that is replicated from a mold cavity usedto form the shaped precursor abrasive particle. Except in the case ofabrasive shards (e.g. as described in U.S. provisional application61/016,965), the shaped abrasive particle will generally have apredetermined geometric shape that substantially replicates the moldcavity that was used to form the shaped abrasive particle. Shapedabrasive particle as used herein excludes abrasive particles obtained bya mechanical crushing operation.

DETAILED DESCRIPTION

Shaped Abrasive Particle with a Sloping Sidewall

Referring to FIGS. 1A, 1B, and 1C an exemplary shaped abrasive particle20 with a sloping sidewall 22 is illustrated. The material from whichthe shaped abrasive particle 20 with a sloping sidewall 22 is madecomprises alpha alumina. Alpha alumina particles can be made from adispersion of aluminum oxide monohydrate that is gelled, molded toshape, dried to retain the shape, calcined, and then sintered asdiscussed herein later. The shaped abrasive particle's shape is retainedwithout the need for a binder to form an agglomerate comprising abrasiveparticles in a binder that are then formed into a shaped structure.

In general, the shaped abrasive particles 20 with a sloping sidewall 22comprise thin bodies having a first face 24, and a second face 26 andhaving a thickness t. The first face 24 and the second face 26 areconnected to each other by at least one sloping sidewall 22. In someembodiments, more than one sloping sidewall 22 can be present and theslope or angle for each sloping sidewall 22 may be the same as shown inFIG. 1A or different as shown in FIG. 4A.

In some embodiments, the first face 24 is substantially planar, thesecond face 26 is substantially planar, or both faces are substantiallyplanar. Alternatively, the faces could be concave or convex as discussedin more detail in copending U.S. application Ser. No. 12/336,961entitled “Dish-Shaped Abrasive Particles With A Recessed Surface”, filedon Dec. 17, 2008. Additionally, an opening or aperture through the facescould be present as discussed in more detail in copending U.S.application Ser. No. 12/337,112 entitled “Shaped Abrasive Particles WithAn Opening”, filed on Dec. 17, 2008.

In one embodiment, the first face 24 and the second face 26 aresubstantially parallel to each other. In other embodiments, the firstface 24 and second face 26 can be nonparallel such that one face issloped with respect to the other face and imaginary lines tangent toeach face would intersect at a point. The sloping sidewall 22 of theshaped abrasive particle 20 with a sloping sidewall 22 can vary and itgenerally forms the perimeter 29 of the first face 24 and the secondface 26. In one embodiment, the perimeter 29 of the first face 24 andsecond face 26 is selected to be a geometric shape, and the first face24 and the second face 26 are selected to have the same geometric shape,although, they differ in size with one face being larger than the otherface. In one embodiment, the perimeter 29 of first face 24 and theperimeter 29 of the second face 26 was a triangular shape that isillustrated.

Referring to FIGS. 1B and 1C, a draft angle α between the second face 26and the sloping sidewall 22 of the shaped abrasive particle 20 can bevaried to change the relative sizes of each face. In various embodimentsof the invention, the draft angle α can be between approximately 95degrees to approximately 130 degrees, or between about 95 degrees toabout 125 degrees, or between about 95 degrees to about 120 degrees, orbetween about 95 degrees to about 115 degrees, or between about 95degrees to about 110 degrees, or between about 95 degrees to about 105degrees, or between about 95 degrees to about 100 degrees. As will beseen in the Examples, specific ranges for the draft angle α have beenfound to produce surprising increases in the grinding performance ofcoated abrasive articles made from the shaped abrasive particles with asloping sidewall.

Referring now to FIG. 1C, a coated abrasive article 40 is shown having afirst major surface 41 of a backing 42 covered by an abrasive layer. Theabrasive layer comprises a make coat 44, and a plurality of shapedabrasive particles 20 with a sloping sidewall 22 attached to the backing42 by the make coat 44. A size coat 46 is applied to further attach oradhere the shaped abrasive particles 20 with a sloping sidewall 22 tothe backing 42.

As seen, the majority of the shaped abrasive particles 20 with a slopingsidewall 22 are tipped or leaning to one side. This results in themajority of the shaped abrasive particles 20 with a sloping sidewall 22having an orientation angle β than 90 degrees relative to the firstmajor surface 41 of the backing 42. This result is unexpected since theelectrostatic coating method of applying the shaped abrasive particleswith a sloping sidewall tends to originally orientate the particles atan orientation angle β of 90 degrees when they are first applied to thebacking. The electrostatic field tends to align the particles verticallywhen applying them to the backing that is located above the shapedabrasive particles with a sloping sidewall. Furthermore, theelectrostatic field tends to accelerate and drive the particles into themake coat at the 90 degree orientation. At some point after the web isturned over, either before or after the size coat 46 is applied, theparticles under the force of gravity or the surface tension of the makeand/or size coat tend to lean over and come to rest on the slopingsidewall 22. It is believed that sufficient time in the process ofmaking the coated abrasive article is present for the shaped abrasiveparticles to lean over and become attached to the make coat by thesloping sidewall 22 before the make coat and size coat cure and hardenpreventing any further rotation. As seen, once the shaped abrasiveparticles with a sloping sidewall are applied and allowed to lean, thevery tips 48 of the shaped abrasive particles have generally the sameheight, h.

To further optimize the leaning orientation, the shaped abrasiveparticles with a sloping sidewall are applied in the backing in an opencoat abrasive layer. A closed coat abrasive layer is defined as themaximum weight of abrasive particles or a blend of abrasive particlesthat can be applied to a make coat of an abrasive article in a singlepass through the maker. An open coat is an amount of abrasive particlesor a blend of abrasive particles, weighing less than the maximum weightin grams that can be applied, that is applied to a make coat of a coatedabrasive article. An open coat abrasive layer will result in less than100% coverage of the make coat with abrasive particles thereby leavingopen areas and a visible resin layer between the particles as best seenin FIG. 3. In various embodiments of the invention, the percent openarea in the abrasive layer can be between about 10% to about 90% orbetween about 30% to about 80%.

It is believed that if too many of the shaped abrasive particles with asloping sidewall are applied to the backing, insufficient spaces betweenthe particles will be present to allow from them to lean or tip prior tocuring the make and size coats. In various embodiments of the invention,greater than 50, 60, 70, 80, or 90 percent of the shaped abrasiveparticles in the coated abrasive article having an open coat abrasivelayer are tipped or leaning having an orientation angle β of less than90 degrees.

Without wishing to be bound by theory, it is believed that anorientation angle β less than 90 degrees results in enhanced cuttingperformance of the shaped abrasive particles with a sloping sidewall.Surprisingly, this result tends to occur regardless of the shapedabrasive particles' rotational orientation about the Z axis within thecoated abrasive article. While FIG. 1C is idealized to show all theparticles aligned in the same direction, an actual coated abrasive discwould have the particles randomly distributed and rotated as best seenin FIG. 3. Since the abrasive disc is rotating and the shaped abrasiveparticles are randomly distributed, some shaped abrasive particles willbe driven into the workpiece at an orientation angle β of less than 90degrees with the workpiece initially striking the second face 26 while aneighboring shaped abrasive particle could be rotated exactly 180degrees with the workpiece striking backside of the shaped abrasiveparticle and the first face 24. With a random distribution of theparticles and the rotation of the disc, less than half of the shapedabrasive particles could have the workpiece initially striking thesecond face 26 instead of the first face 24. However, for an abrasivebelt having a defined direction of rotation and a defined point ofcontact with the workpiece, it may be possible to align the shapedabrasive particles with a sloping sidewall on the belt to ensure thateach shaped abrasive particle runs at an orientation angle β of lessthan 90 degrees and that the workpiece is driven into the second face 26first as idealized in FIG. 1C. In various embodiments of the invention,the orientation angle β for at least a majority of the shaped abrasiveparticles with a sloping sidewall in an abrasive layer of a coatedabrasive article can be between about 50 degrees to about 85 degrees, orbetween about 55 degrees to about 85 degrees, or between about 60degrees to about 85 degrees, or between about 65 degrees to about 85degrees, or between about 70 degrees to about 85 degrees, or betweenabout 75 degrees to about 85 degrees, or between about 80 degrees toabout 85 degrees.

Referring now to FIGS. 2 and 3, photomicrographs of shaped abrasiveparticles 20 with a sloping sidewall 22 are shown. In FIG. 3 the draftangle α is approximately 120 degrees and the shaped abrasive particlescomprised an equilateral triangle. The sides of each triangle measuredapproximately 1.6 mm at the perimeter of the larger first face 24. Theshaped abrasive particles had a thickness of approximately 0.38 mm. Thesurface of the resulting coated abrasive disc made from the shapedabrasive particles of FIG. 2 is shown in FIG. 3. As seen, the majorityof the shaped abrasive particles are resting in the make coat on one ofthe sloping sidewalls. The orientation angle β for the majority of theshaped abrasive particles with a sloping sidewall in the abrasive layerof the coated abrasive article in FIG. 3 is approximately 60 degrees.

Referring to FIGS. 4A-C, a second embodiment of the shaped abrasiveparticle 20 with a sloping sidewall 22 is illustrated. The material fromwhich the shaped abrasive particle 20 with a sloping sidewall 22 is madecomprises alpha alumina. Alpha alumina particles can be made from adispersion of aluminum oxide monohydrate that is gelled, molded toshape, dried to retain the shape, calcined, and then sintered asdiscussed herein later. The shaped abrasive particle's shape is retainedwithout the need for a binder to form an agglomerate comprising abrasiveparticles in a binder that are then formed into a shaped structure.

In general, the shaped abrasive particles 20 with a sloping sidewall 22comprise thin bodies having a first face 24, and a second face 26 andhaving a thickness t. The first face 24 and the second face 26 areconnected to each other by at least a first sloping sidewall 50 having afirst draft angle 52 and by a second sloping sidewall 54 having a seconddraft angle 56, which is selected to be a different value from the firstdraft angle. In the illustrated embodiment, the first and second facesare also connected by a third sloping sidewall 58 having a third draftangle 60, which is a different value from either of the other two draftangles.

In the illustrated embodiment, the first, second and third draft anglesare all different values from each other. For example, the first draftangle 52 could be 120 degrees, the second draft angle 56 could be 110degrees, and the third draft angle 60 could be 100 degrees. Theresulting coated abrasive article 40, as shown in FIG. 4C, made from theshaped abrasive particles with the three different draft angles willtend to have an even distribution of shaped abrasive particles landingon each of the three different sloping sidewalls. As such, the coatedabrasive article will tend to have three distinct heights for the tips48 of the shaped abrasive particles from the backing. The first slopingsidewall 50 contacting the make coat with the largest draft angle willhave the lowest tip height, h1, the second sloping sidewall 54 with theintermediate draft angle will have an intermediate tip height, h2, andthe third sloping sidewall, 58, with the smallest draft angle will havethe highest tip height, h3. As a result, the coated abrasive articlewill possess shaped abrasive particles having three distinct orientationangles β relative to the backing and three distinct tip heights. It isbelieved that such a coated abrasive article will possess more uniformcutting performance as the abrasive article wears due to the unusedshorter tips of the shaped abrasive particles coming into contact withthe workpiece as the taller tips of the shaped abrasive particles tendto wear down and dull.

In some embodiments, the first face 24 is substantially planar, thesecond face 26 is substantially planar, or both faces are substantiallyplanar. Alternatively, the faces could be concave or convex as discussedin more detail in copending U.S. application Ser. No. 12/336,961entitled “Dish-Shaped Abrasive Particles With A Recessed Surface”, filedon Dec. 17, 2008. Additionally, an opening or aperture through the facescould be present as discussed in more detail in copending U.S.application Ser. No. 12/337,112 entitled “Shaped Abrasive Particles WithAn Opening”, filed on Dec. 17, 2008.

In one embodiment, the first face 24 and the second face 26 aresubstantially parallel to each other. In other embodiments, the firstface 24 and second face 26 can be nonparallel such that one face issloped with respect to the other face and imaginary lines tangent toeach face would intersect at a point. The first, second, and thirdsloping sidewalls of the shaped abrasive particle 20 with a slopingsidewall 22 can vary and they generally form the perimeter 29 of thefirst face 24 and the second face 26. In one embodiment, the perimeter29 of the first face 24 and the second face 26 is selected to be ageometric shape, and the first face 24 and the second face 26 areselected to have the same geometric shape, although, they differ in sizewith one face being larger than the other face. In one embodiment, theperimeter 29 of first face 24 and the perimeter 29 of the second face 26was a triangular shape that is illustrated.

Referring to FIGS. 4B and 4C, the first, second, and third, draft anglesbetween the second face 26 and the respective sloping sidewall of theshaped abrasive particle 20 can be varied with at least two of the draftangles being different values, and desirably all three being differentvalues. In various embodiments of the invention, the first draft angle,the second draft angle, and the third draft angle can be between about95 degrees to about 130 degrees, or between about 95 degrees to about125 degrees, or between about 95 degrees to about 120 degrees, orbetween about 95 degrees to about 115 degrees, or between about 95degrees to about 110 degrees, or between about 95 degrees to about 105degrees, or between about 95 degrees to about 100 degrees.

Referring now to FIG. 4C, a coated abrasive article 40 is shown having afirst major surface 41 of a backing 42 covered by an abrasive layer. Theabrasive layer comprises a make coat 44, and a plurality of shapedabrasive particles 20 with either the first, the second, or the thirdsloping sidewall attached to the backing 42 by the make coat 44. A sizecoat 46 is applied to further attach or adhere the shaped abrasiveparticles 20 with a sloping sidewall 22 to the backing 42.

As seen, the majority of the shaped abrasive particles 20 with a slopingsidewall 22 are tipped or leaning to one side. This results in themajority of the shaped abrasive particles 20 with a sloping sidewall 22having an orientation angle β less than 90 degrees relative to the firstmajor surface 41 of the backing 42 as previously discussed for the firstembodiment.

To further optimize the leaning orientation, the shaped abrasiveparticles with a sloping sidewall are applied in the backing in an opencoat abrasive layer. An open coat abrasive layer will result in lessthan 100% coverage of the make coat with abrasive particles therebyleaving open areas and a visible resin layer between the abrasiveparticles as best seen in FIG. 3. In various embodiments of theinvention, the percent open area in the abrasive layer can be betweenabout 10% to about 90% or between about 30% to about 80%.

It is believed that if too many of the shaped abrasive particles with asloping sidewall are applied to the backing, insufficient spaces betweenthe shaped abrasive particles will be present to allow for them to leanor tip prior to curing the make and size coats. In various embodimentsof the invention, greater than 50, 60, 70, 80, or 90 percent of theshaped abrasive particles in the coated abrasive article having an opencoat abrasive layer are tipped or leaning having an orientation angle βof less than 90 degrees.

Without wishing to be bound by theory, it is believed that anorientation angle β of less than 90 degrees results in enhanced cuttingperformance of the shaped abrasive particles with a sloping sidewall aspreviously discussed. In various embodiments of the invention, theorientation angle β for at least a majority of the shaped abrasiveparticles with a sloping sidewall in an abrasive layer of a coatedabrasive article can be between about 50 degrees to about 85 degrees, orbetween about 55 degrees to about 85 degrees, or between about 60degrees to about 85 degrees, or between about 65 degrees to about 85degrees, or between about 70 degrees to about 85 degrees, or betweenabout 75 degrees to about 85 degrees, or between about 80 degrees toabout 85 degrees.

Referring now to FIGS. 5A-B a third embodiment of the invention isshown. In this embodiment, the sloping sidewall 22 is defined by aradius, R, instead of the draft angle α for the embodiment shown inFIGS. 1A-1C. A sloping sidewall 22 defined by a radius, R, has also beenfound to result in the shaped abrasive particles 20 tipping or leaningwhen forming a coated abrasive article as shown in FIG. 5C. Grindingtests have shown that shaped abrasive particles comprising anequilateral triangle with the sides of each triangle measuringapproximately 1.6 mm at the perimeter of the larger first face 24, andhaving a thickness of approximately 0.38 mm, have the same cutperformance with a draft angle of 120 degrees or a radius, R, of 0.51mm. In various embodiment of the invention, the radius, R, can bebetween about 0.5 to about 2 times the thickness, t, of the shapedabrasive particle.

As with the second embodiment, the radius, R, can be varied for each ofthe sidewalls to result in shaped abrasive particles leaning or tippingto varying degrees in the coated abrasive article.

It is believed that if too many of the shaped abrasive particles with asloping sidewall are applied to the backing, insufficient spaces betweenthe shaped abrasive particles will be present to allow for them to leanor tip prior to curing the make and size coats. In various embodimentsof the invention, greater than 50, 60, 70, 80, or 90 percent of theshaped abrasive particles in the coated abrasive article having an opencoat abrasive layer are tipped or leaning having an orientation angle βof less than 90 degrees.

For either the first embodiment, the second embodiment, or the thirdembodiment, the shaped abrasive particles 20 with a sloping sidewall 22can have various three-dimensional shapes. The geometric shape of theperimeter 29 can be triangular, rectangular, circular, elliptical,star-shaped or that of other regular or irregular polygons. In oneembodiment, an equilateral triangle is used and in another embodiment,an isosceles triangle is used. For the purpose of this disclosure, asubstantially triangular shape also includes three-sided polygonswherein one or more of the sides can be arcuate and/or the tips of thetriangle can be arcuate.

Additionally, the various sloping sidewalls of the shaped abrasiveparticles can have the same draft angle or different draft angles.Furthermore, a draft angle of 90 degrees can be used on one or moresidewalls as long as one of the sidewalls is a sloping sidewall having adraft angle of about 95 degrees or greater.

The shaped abrasive particles 20 with a sloping sidewall can havevarious volumetric aspect ratios. The volumetric aspect ratio is definedas the ratio of the maximum cross sectional area passing through thecentroid of a volume divided by the minimum cross sectional area passingthrough the centroid. For some shapes, the maximum or minimum crosssectional area may be a plane tipped, angled, or tilted with respect tothe external geometry of the shape. For example, a sphere would have avolumetric aspect ratio of 1.000 while a cube will have a volumetricaspect ratio of 1.414. A shaped abrasive particle in the form of anequilateral triangle having each side equal to length A and a uniformthickness equal to A will have a volumetric aspect ratio of 1.54, and ifthe uniform thickness is reduced to 0.25 A, the volumetric aspect ratiois increased to 2.64. It is believed that shaped abrasive particleshaving a larger volumetric aspect ratio have enhanced cuttingperformance. In various embodiments of the invention, the volumetricaspect ratio for the shaped abrasive particles with a sloping sidewallcan be greater than about 1.15, or greater than about 1.50, or greaterthan about 2.0, or between about 1.15 to about 10.0, or between about1.20 to about 5.0, or between about 1.30 to about 3.0.

The shaped abrasive particles with a sloping sidewall can have a muchsmaller radius of curvature at the points or corners of the shapedabrasive particles. The equilateral triangular shaped abrasive particlesdisclosed in U.S. Pat. No. 5,366,523 to Rowenhorst et al. and picturedin FIG. 8, had a radius of curvature for the points of the triangle(measured from one side around the point to the next side) of 103.6microns for the average tip radius. The radius of curvature can bemeasured from a polished cross-section of the first or second face usingimage analysis such as a Clemex Image Analysis program interfaced withan inverted light microscope or other suitable image analysis software.The radius of curvature for each triangular apex can be estimated bydefining three points at each apex when viewed in cross section at 100×magnification. A point is placed at the start of the tip's curve wherethere is a transition from the straight edge to the start of a curve, atthe apex of the tip, and at the transition from the curved tip back to astraight edge. The image analysis software then draws an arc defined bythe three points (start, middle, and end of the curve) and calculates aradius of curvature. The radius of curvature for at least 30 apexes aremeasured and averaged to determine the average tip radius. The shapedabrasive particles made by the current method are much more preciselymade as best seen by comparing FIG. 2 to FIG. 8. As such, the averagetip radius for the shaped abrasive particles is much less. The averagetip radius for shaped abrasive particles made according to the presentdisclosure has been measured to be less than 19.2 microns. In variousembodiments of the invention, the average tip radius can be less than 75microns, or less than 50 microns, or less than 25 microns. It isbelieved that a sharper tip promotes more aggressive cutting an improvedfracturing of the shaped abrasive particles during use.

In addition to having a sharper tip, the shaped abrasive particles canhave a much more precisely defined sidewall. Referring now to FIGS. 9and 10, photomicrographs of polished cross sections taken perpendicularthrough the faces of the prior art shaped abrasive particles of FIG. 8are shown. As seen, the sidewall (top surface) tends to be eitherconcave or convex and is not uniformly planar. Depending on where youtake the cross section, the same sidewall may transition from one shapeto another. Referring to FIG. 10, in the foreground the sidewall isconvex while in the background it is concave.

Referring to FIG. 11, a polished cross section taken perpendicularthrough the faces of a shaped abrasive particle with a sloping sidewallhaving a 98 degree draft angle is shown. The first face 24 (right handvertical surface) is concave as disclosed in the pending patentapplication attorney docket number 64716US002 referred to above. Aconcave surface is thought to enhance grinding performance by removingmore material during use similar to a scoop, spoon, or hollow groundchisel blade. The second face 26 is substantially planar (left handvertical surface). Finally, the sidewall (top surface) is uniformlyplanar. By uniformly planar it is meant that the sidewall does not haveareas that are convex from one face to the other face, or areas that areconcave from one face to the other face and at least 50%, or at least75%, or at least 85% or more of the sidewall surface is planar. As seenin the cross section, when the sidewall is cut at a 90 degree angle andpolished, a substantially linear edge appears (where the top sidewallsurface meets the cut cross section's front surface). The uniformlyplanar sidewall would typically have that substantially linear edge atsubstantially all cross sectional planes along the length of thesidewall. The uniformly planar sidewall provides better defined(sharper) edges where the sidewall intersects with the first face andthe second face, and this is also thought to enhance grindingperformance.

Shaped abrasive particles 20 with a sloping sidewall 22 made accordingto the present disclosure can be incorporated into an abrasive article,or used in loose form. Abrasive particles are generally graded to agiven particle size distribution before use. Such distributionstypically have a range of particle sizes, from coarse particles to fineparticles. In the abrasive art this range is sometimes referred to as a“coarse”, “control”, and “fine” fractions. Abrasive particles gradedaccording to abrasive industry accepted grading standards specify theparticle size distribution for each nominal grade within numericallimits. Such industry accepted grading standards (i.e., abrasiveindustry specified nominal grade) include those known as the AmericanNational Standards Institute, Inc. (ANSI) standards, Federation ofEuropean Producers of Abrasive Products (FEPA) standards, and JapaneseIndustrial Standard (JIS) standards.

ANSI grade designations (i.e., specified nominal grades) include: ANSI4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI 36, ANSI 40, ANSI 50, ANSI 60,ANSI 80, ANSI 100, ANSI 120, ANSI 150, ANSI 180, ANSI 220, ANSI 240,ANSI 280, ANSI 320, ANSI 360, ANSI 400, and ANSI 600. FEPA gradedesignations include P8, P12, P16, P24, P36, P40, P50, P60, P80, P100,P120, P150, P180, P220, P320, P400, P500, P600, P800, P1000, and P1200.JIS grade designations include JIS8, JIS12, JIS16, JIS24, JIS36, JIS46,JIS54, JIS60, JIS80, JIS100, JIS150, JIS180, JIS220, JIS240, JIS280,JIS320, JIS360, JIS400, JIS600, JIS800, JIS1000, JIS1500, JIS2500,JIS4000, JIS6000, JIS8000, and JIS10,000.

Alternatively, the shaped abrasive particles 20 with a sloping sidewall22 can graded to a nominal screened grade using U.S.A. Standard TestSieves conforming to ASTM E-11 “Standard Specification for Wire Clothand Sieves for Testing Purposes.” ASTM E-11 proscribes the requirementsfor the design and construction of testing sieves using a medium ofwoven wire cloth mounted in a frame for the classification of materialsaccording to a designated particle size. A typical designation may berepresented as −18+20 meaning that the shaped abrasive particles 20 passthrough a test sieve meeting ASTM E-11 specifications for the number 18sieve and are retained on a test sieve meeting ASTM E-11 specificationsfor the number 20 sieve. In one embodiment, the shaped abrasiveparticles 20 with a sloping sidewall 22 have a particle size such thatmost of the particles pass through an 18 mesh test sieve and can beretained on a 20, 25, 30, 35, 40, 45, or 50 mesh test sieve. In variousembodiments of the invention, the shaped abrasive particles 20 with asloping sidewall 22 can have a nominal screened grade comprising:−18+20, −20+25, −25+30, −30+35, −35+40, −40+45, −45+50, −50+60, −60+70,−70+80, −80+100, −100+120, −120+140, −140+170, −170+200, −200+230,−230+270, −270+325, −325+400, −400+450, −450+500, or −500+635.

In one aspect, the present disclosure provides a plurality of shapedabrasive particles having an abrasives industry specified nominal gradeor nominal screened grade, wherein at least a portion of the pluralityof abrasive particles are shaped abrasive particles 20 with a slopingsidewall 22. In another aspect, the disclosure provides a methodcomprises grading the shaped abrasive particles 20 with a slopingsidewall 22 made according to the present disclosure to provide aplurality of shaped abrasive particles 20 with a sloping sidewall 22having an abrasives industry specified nominal grade or a nominalscreened grade.

If desired, the shaped abrasive particles 20 with a sloping sidewall 22having an abrasives industry specified nominal grade or a nominalscreened grade can be mixed with other known abrasive or non-abrasiveparticles. In some embodiments, at least 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100 percent byweight of the plurality of abrasive particles having an abrasivesindustry specified nominal grade or a nominal screened grade are shapedabrasive particles 20 with a sloping sidewall 22 made according to thepresent disclosure, based on the total weight of the plurality ofabrasive particles.

Particles suitable for mixing with the shaped abrasive particles 20 witha sloping sidewall 22 include conventional abrasive grains, diluentgrains, or erodable agglomerates, such as those described in U.S. Pat.Nos. 4,799,939 and 5,078,753. Representative examples of conventionalabrasive grains include fused aluminum oxide, silicon carbide, garnet,fused alumina zirconia, cubic boron nitride, diamond, and the like.Representative examples of diluent grains include marble, gypsum, andglass. Blends of differently shaped abrasive particles 20 with a slopingsidewall 22 (triangles and squares for example) or blends of shapedabrasive particles 20 with different draft angles (for example particleshaving an 98 degree draft angle mixed with particles having a 120 degreedraft angle) can be used in the articles of this invention.

The shaped abrasive particles 20 with a sloping sidewall 22 may alsohave a surface coating. Surface coatings are known to improve theadhesion between abrasive grains and the binder in abrasive articles orcan be used to aid in electrostatic deposition of the shaped abrasiveparticles 20. Such surface coatings are described in U.S. Pat. Nos.5,213,591; 5,011,508; 1,910,444; 3,041,156; 5,009,675; 5,085,671;4,997,461; and 5,042,991. Additionally, the surface coating may preventthe shaped abrasive particle from capping. Capping is the term todescribe the phenomenon where metal particles from the workpiece beingabraded become welded to the tops of the shaped abrasive particles.Surface coatings to perform the above functions are known to those ofskill in the art.

Abrasive Article Having Shaped Abrasive Particles With A SlopingSidewall

Referring to FIGS. 1C, 4C, and 5C, a coated abrasive article 40comprises a backing 42 having a first layer of binder, hereinafterreferred to as the make coat 44, applied over a first major surface 41of backing 42. Attached or partially embedded in the make coat 44 are aplurality of shaped abrasive particles 20 with a sloping sidewall 22forming an abrasive layer. Over the shaped abrasive particles 20 with asloping sidewall 22 is a second layer of binder, hereinafter referred toas the size coat 46. The purpose of make coat 44 is to secure shapedabrasive particles 20 with n sloping sidewall 22 to backing 42 and thepurpose of size coat 46 is to reinforce shaped abrasive particles 20with a sloping sidewall 22. The majority of the shaped abrasiveparticles 20 with a sloping sidewall 22 are oriented such that the tip48 or vertex points away from the backing 42 and the shaped abrasiveparticles are resting on the sloping sidewall 22 and tipped or leaningas shown.

The make coat 44 and size coat 46 comprise a resinous adhesive. Theresinous adhesive of the make coat 44 can be the same as or differentfrom that of the size coat 46. Examples of resinous adhesives that aresuitable for these coats include phenolic resins, epoxy resins,urea-formaldehyde resins, acrylate resins, aminoplast resins, melamineresins, acrylated epoxy resins, urethane resins and combinationsthereof. In addition to the resinous adhesive, the make coat 44 or sizecoat 46, or both coats, may further comprise additives that are known inthe art, such as, for example, fillers, grinding aids, wetting agents,surfactants, dyes, pigments, coupling agents, adhesion promoters, andcombinations thereof. Examples of fillers include calcium carbonate,silica, talc, clay, calcium metasilicate, dolomite, aluminum sulfate andcombinations thereof.

A grinding aid can be applied to the coated abrasive article. A grindingaid is defined as particulate material, the addition of which has asignificant effect on the chemical and physical processes of abrading,thereby resulting in improved performance. Grinding aids encompass awide variety of different materials and can be inorganic or organic.Examples of chemical groups of grinding aids include waxes, organichalide compounds, halide salts, and metals and their alloys. The organichalide compounds will typically break down during abrading and release ahalogen acid or a gaseous halide compound. Examples of such materialsinclude chlorinated waxes, such as tetrachloronaphthalene,pentachloronaphthalene; and polyvinyl chloride. Examples of halide saltsinclude sodium chloride, potassium cryolite, sodium cryolite, ammoniumcryolite, potassium tetrafluoroborate, sodium tetrafluoroborate, siliconfluorides, potassium chloride, magnesium chloride. Examples of metalsinclude tin, lead, bismuth, cobalt, antimony, cadmium, iron, andtitanium. Other grinding aids include sulfur, organic sulfur compounds,graphite, and metallic sulfides. It is also within the scope of thisinvention to use a combination of different grinding aids; in someinstances, this may produce a synergistic effect. In one embodiment, thegrinding aid was cryolite or potassium tetrafluoroborate. The amount ofsuch additives can be adjusted to give desired properties. It is alsowithin the scope of this invention to utilize a supersize coating. Thesupersize coating typically contains a binder and a grinding aid. Thebinders can be formed from such materials as phenolic resins, acrylateresins, epoxy resins, urea-formaldehyde resins, melamine resins,urethane resins, and combinations thereof.

It is also within the scope of this invention that the shaped abrasiveparticles 20 with a sloping sidewall 22 can be utilized in a bondedabrasive article, a nonwoven abrasive article, or abrasive brushes. Abonded abrasive can comprises a plurality of the shaped abrasiveparticles 20 with a sloping sidewall 22 bonded together by means of abinder to form a shaped mass. The binder for a bonded abrasive can bemetallic, organic, or vitreous. A nonwoven abrasive comprises aplurality of the shaped abrasive particles 20 with a sloping sidewall 22bonded into a fibrous nonwoven web by means of an organic binder.

Method of Making Shaped Abrasive Particles with a Sloping Sidewall

The first process step involves providing either a seeded on un-seededabrasive dispersion that can be converted into alpha alumina. The alphaalumina precursor composition often comprises a liquid that is avolatile component. In one embodiment, the volatile component is water.The abrasive dispersion should comprise a sufficient amount of liquidfor the viscosity of the abrasive dispersion to be sufficiently low toenable filling the mold cavities and replicating the mold surfaces, butnot so much liquid as to cause subsequent removal of the liquid from themold cavity to be prohibitively expensive. In one embodiment, theabrasive dispersion comprises from 2 percent to 90 percent by weight ofthe particles that can be converted into alpha alumina, such asparticles of aluminum oxide monohydrate (boehmite), and at least 10percent by weight, or from 50 percent to 70 percent, or 50 percent to 60percent, by weight of the volatile component such as water. Conversely,the abrasive dispersion in some embodiments contains from 30 percent to50 percent, or 40 percent to 50 percent, by weight solids.

Aluminum oxide hydrates other than boehmite can also be used. Boehmitecan be prepared by known techniques or can be obtained commercially.Examples of commercially available boehmite include products having thetrademarks “DISPERAL”, and “DISPAL”, both available from Sasol NorthAmerica, Inc. or “HiQ-40” available from BASF Corporation. Thesealuminum oxide monohydrates are relatively pure, i.e., they includerelatively little, if any, hydrate phases other than monohydrates, andhave a high surface area. The physical properties of the resultingshaped abrasive particles 20 with a sloping sidewall 22 will generallydepend upon the type of material used in the abrasive dispersion.

In one embodiment, the abrasive dispersion is in a gel state. As usedherein, a “gel” is a three dimensional network of solids dispersed in aliquid. The abrasive dispersion may contain a modifying additive orprecursor of a modifying additive. The modifying additive can functionto enhance some desirable property of the abrasive particles or increasethe effectiveness of the subsequent sintering step. Modifying additivesor precursors of modifying additives can be in the form of solublesalts, typically water soluble salts. They typically consist of ametal-containing compound and can be a precursor of oxide of magnesium,zinc, iron, silicon, cobalt, nickel, zirconium, hafnium, chromium,yttrium, praseodymium, samarium, ytterbium, neodymium, lanthanum,gadolinium, cerium, dysprosium, erbium, titanium, and mixtures thereof.The particular concentrations of these additives that can be present inthe abrasive dispersion can be varied based on skill in the art.Typically, the introduction of a modifying additive or precursor of amodifying additive will cause the abrasive dispersion to gel. Theabrasive dispersion can also be induced to gel by application of heatover a period of time.

The abrasive dispersion can also contain a nucleating agent to enhancethe transformation of hydrated or calcined aluminum oxide to alphaalumina. Nucleating agents suitable for this disclosure include fineparticles of alpha alumina, alpha ferric oxide or its precursor,titanium oxides and titanates, chrome oxides, or any other material thatwill nucleate the transformation. The amount of nucleating agent, ifused, should be sufficient to effect the transformation of alphaalumina. Nucleating such abrasive dispersions is disclosed in U.S. Pat.No. 4,744,802 to Schwabel.

A peptizing agent can be added to the abrasive dispersion to produce amore stable hydrosol or colloidal abrasive dispersion. Suitablepeptizing agents are monoprotic acids or acid compounds such as aceticacid, hydrochloric acid, formic acid, and nitric acid. Multiprotic acidscan also be used but they can rapidly gel the abrasive dispersion,making it difficult to handle or to introduce additional componentsthereto. Some commercial sources of boehmite contain an acid titer (suchas absorbed formic or nitric acid) that will assist in forming a stableabrasive dispersion.

The abrasive dispersion can be formed by any suitable means, such as,for example, simply by mixing aluminum oxide monohydrate with watercontaining a peptizing agent or by forming an aluminum oxide monohydrateslurry to which the peptizing agent is added. Defoamers or othersuitable chemicals can be added to reduce the tendency to form bubblesor entrain air while mixing. Additional chemicals such as wettingagents, alcohols, or coupling agents can be added if desired. The alphaalumina abrasive grain may contain silica and iron oxide as disclosed inU.S. Pat. No. 5,645,619 to Erickson et al. on Jul. 8, 1997. The alphaalumina abrasive grain may contain zirconia as disclosed in U.S. Pat.No. 5,551,963 to Larmie on Sep. 3, 1996. Alternatively, the alphaalumina abrasive grain can have a microstructure or additives asdisclosed in U.S. Pat. No. 6,277,161 to Castro on Aug. 21, 2001.

The second process step involves providing a mold having at least onemold cavity, and preferably a plurality of cavities. The mold can have agenerally planar bottom surface and a plurality of mold cavities. Theplurality of cavities can be formed in a production tool. The productiontool can be a belt, a sheet, a continuous web, a coating roll such as arotogravure roll, a sleeve mounted on a coating roll, or die. Theproduction tool comprises polymeric material. Examples of suitablepolymeric materials include thermoplastics such as polyesters,polycarbonates, poly(ether sulfone), poly(methyl methacrylate),polyurethanes, polyvinylchloride, polyolefins, polystyrene,polypropylene, polyethylene or combinations thereof, or thermosettingmaterials. In one embodiment, the entire tooling is made from apolymeric or thermoplastic material. In another embodiment, the surfacesof the tooling in contact with the sol-gel while drying, such as thesurfaces of the plurality of cavities, comprises polymeric orthermoplastic materials and other portions of the tooling can be madefrom other materials. A suitable polymeric coating may be applied to ametal tooling to change its surface tension properties by way ofexample.

A polymeric or thermoplastic tool can be replicated off a metal mastertool. The master tool will have the inverse pattern desired for theproduction tool. The master tool can be made in the same manner as theproduction tool. In one embodiment, the master tool is made out ofmetal, e.g., nickel and is diamond turned. The polymeric sheet materialcan be heated along with the master tool such that the polymericmaterial is embossed with the master tool pattern by pressing the twotogether. A polymeric or thermoplastic material can also be extruded orcast onto the master tool and then pressed. The thermoplastic materialis cooled to solidify and produce the production tool. If athermoplastic production tool is utilized, then care should be taken notto generate excessive heat that may distort the thermoplastic productiontool limiting its life. More information concerning the design andfabrication of production tooling or master tools can be found in U.S.Pat. Nos. 5,152,917 (Pieper et al.); 5,435,816 (Spurgeon et al.);5,672,097 (Hoopman et al.); 5,946,991 (Hoopman et al.); 5,975,987(Hoopman et al.); and 6,129,540 (Hoopman et al.).

Access to cavities can be from an opening in the top surface or bottomsurface of the mold. In some instances, the cavity can extend for theentire thickness of mold. Alternatively, the cavity can extend only fora portion of the thickness of the mold. In one embodiment, the topsurface is substantially parallel to bottom surface of the mold with thecavities having a substantially uniform depth. At least one side of themold, i.e. the side in which the cavity is formed, can remain exposed tothe surrounding atmosphere during the step in which the volatilecomponent is removed.

The cavity has a specified three-dimensional shape. In one embodiment,the shape of a cavity can be described as being a triangle, as viewedfrom the top, having a sloping sidewall such that the bottom surface ofthe cavity is slightly smaller than the opening in the top surface. Asloping sidewall is believed to enhance grinding performance and enableeasier removal of the precursor abrasive particles from the mold. Inanother embodiment, the mold comprised a plurality of triangularcavities. Each of the plurality of triangular cavities comprises anequilateral triangle.

Alternatively, other cavity shapes can be used, such as, circles,rectangles, squares, hexagons, stars, or combinations thereof, allhaving a substantially uniform depth dimension. The depth dimension isequal to the perpendicular distance from the top surface to thelowermost point on the bottom surface. The depth of a given cavity canbe uniform or can vary along its length and/or width. The cavities of agiven mold can be of the same shape or of different shapes.

The third process step involves filling the cavities in the mold withthe abrasive dispersion by any conventional technique. In someembodiments, a knife roll coater or vacuum slot die coater can be used.A mold release can be used to aid in removing the particles from themold if desired. Typical mold release agents include oils such as peanutoil or mineral oil, fish oil, silicones, polytetrafluoroethylene, zincsterate, and graphite. In general, between about 0.1% to about 5% byweight mold release agent, such as peanut oil, in a liquid, such aswater or alcohol, is applied to the surfaces of the production toolingin contact with the sol-gel such that between about 0.1 mg/in² to about3.0 mg/in², or between about 0.1 mg/in² to about 5.0 mg/in² of the moldrelease agent is present per unit area of the mold when a mold releaseis desired. In one embodiment, the top surface of the mold is coatedwith the abrasive dispersion. The abrasive dispersion can be pumped ontotop surface. Next, a scraper or leveler bar can be used to force theabrasive dispersion fully into the cavity of the mold. The remainingportion of the abrasive dispersion that does not enter cavity can beremoved from top surface of the mold and recycled. In some embodiments,a small portion of the abrasive dispersion can remain on top surface andin other embodiments the top surface is substantially free of thedispersion. The pressure applied by the scraper or leveler bar istypically less than 100 psi, or less than 50 psi, or less than 10 psi.In some embodiments, no exposed surface of the abrasive dispersionextends substantially beyond the top surface to ensure uniformity inthickness of the resulting shaped abrasive particles 20.

The fourth process step involves removing the volatile component to drythe dispersion. Desirably, the volatile component is removed by fastevaporation rates. In some embodiments, removal of the volatilecomponent by evaporation occurs at temperatures above the boiling pointof the volatile component. An upper limit to the drying temperatureoften depends on the material the mold is made from. For polypropylenetooling the temperature should be less than the melting point of theplastic.

In one embodiment, for a water dispersion of between about 40 to 50percent solids and a polypropylene mold, the drying temperatures can bebetween about 90 degrees C. to about 165 degrees C., or between about105 degrees C. to about 150 degrees C., or between about 105 degrees C.to about 120 degrees C. Higher temperatures can lead to the formation oflarger openings but can also lead to degradation of the polypropylenetooling limiting its useful life as a mold.

In one embodiment, a sample of boehmite sol-gel was made using thefollowing recipe: aluminum oxide monohydrate powder (1600 parts) havingthe trade designation “DISPERAL” was dispersed by high shear mixing asolution containing water (2400 parts) and 70% aqueous nitric acid (72parts) for 11 minutes. The resulting sol-gel was aged for at least 1hour before coating. The sol-gel was forced into production toolinghaving triangular shaped mold cavities of 28 mils depth and 110 mils oneach side and having a sloping sidewall having a predetermined draftangel a between the sidewall and bottom of the mold.

The sol-gel was forced into the cavities with a putty knife so that theopenings of the production tooling were completely filled. A moldrelease agent, 1% peanut oil in methanol was used to coat the productiontooling such that about 0.5 mg/in² of peanut oil was applied to the moldsurfaces. The excess methanol was removed by placing sheets of theproduction tooling in an air convection oven for 5 minutes at 45 C. Thesol-gel coated production tooling was placed in an air convection ovenat 45 C for at least 45 minutes to dry. The precursor shaped abrasiveparticles were removed from the production tooling by passing it over anultrasonic horn. These precursor shaped abrasive particles can be firedto produce shaped abrasive particles 20 with a sloping sidewall 22.

The fifth process step involves removing the precursor shaped abrasiveparticles with a sloping sidewall from the mold cavities. The precursorshaped abrasive particles with a sloping sidewall can be removed fromthe cavities by using the following processes alone or in combination onthe mold: gravity, vibration, ultrasonic vibration, vacuum, orpressurized air to remove the particles from the mold cavities.

The precursor abrasive particles with a sloping sidewall can be furtherdried outside of the mold. If the abrasive dispersion is dried to thedesired level in the mold, this additional drying step is not necessary.However, in some instances it may be economical to employ thisadditional drying step to minimize the time that the abrasive dispersionresides in the mold. Typically, the precursor shaped abrasive particleswill be dried from 10 to 480 minutes, or from 120 to 400 minutes, at atemperature from 50 degrees C. to 160 degrees C., or at 120 degrees C.to 150 degrees C.

The sixth process step involves calcining the precursor shaped abrasiveparticles with a sloping sidewall 22. During calcining, essentially allthe volatile material is removed, and the various components that werepresent in the abrasive dispersion are transformed into metal oxides.The precursor shaped abrasive particles are generally heated to atemperature from 400 degrees C. to 800 degrees C., and maintained withinthis temperature range until the free water and over 90 percent byweight of any bound volatile material are removed. In an optional step,it may be desired to introduce the modifying additive by an impregnationprocess. A water-soluble salt can be introduced by impregnation into thepores of the calcined, precursor shaped abrasive particles. Then theprecursor shaped abrasive particles are prefired again. This option isfurther described in European Patent Application No. 293,163.

The seventh process step involves sintering the calcined, precursorshaped abrasive particles to form alpha alumina particles. Prior tosintering, the calcined, precursor shaped abrasive particles are notcompletely densified and thus lack the desired hardness to be used asshaped abrasive particles. Sintering takes place by heating thecalcined, precursor shaped abrasive particles to a temperature of from1,000 degrees C. to 1,650 degrees C. and maintaining them within thistemperature range until substantially all of the alpha aluminamonohydrate (or equivalent) is converted to alpha alumina and theporosity is reduced to less than 15 percent by volume. The length oftime to which the calcined, precursor shaped abrasive particles must beexposed to the sintering temperature to achieve this level of conversiondepends upon various factors but usually from five seconds to 48 hoursis typical.

In another embodiment, the duration for the sintering step ranges fromone minute to 90 minutes. After sintering, the shaped abrasive particleswith a sloping sidewall can have a Vickers hardness of 10 GPa, 16 GPa,18 GPa, 20 GPa, or greater.

Other steps can be used to modify the described process, such as rapidlyheating the material from the calcining temperature to the sinteringtemperature, centrifuging the abrasive dispersion to remove sludge,waste, etc. Moreover, the process can be modified by combining two ormore of the process steps if desired. Conventional process steps thatcan be used to modify the process of this disclosure are more fullydescribed in U.S. Pat. No. 4,314,827 to Leitheiser. Additionally, theshaped abrasive particles with a sloping sidewall can have grooves onone of the faces as described in copending application U.S. Ser. No.12/627,567 entitled “Shaped Abrasive Particles With Grooves”, and filedon Dec. 17, 2008. The grooves are formed by a plurality of ridges in thebottom surface of the mold cavity that have been found to make it easierto remove the precursor shaped abrasive particles from the mold. Moreinformation concerning methods to make shaped abrasive particles isdisclosed in U.S. patent application Ser. No. 12/337,001 entitled“Method Of Making Abrasive Shards, Shaped Abrasive Particles With AnOpening, Or Dish-Shaped Abrasive Particles”, and filed on Dec. 17, 2008.

EXAMPLES

Objects and advantages of this disclosure are further illustrated by thefollowing non-limiting examples. The particular materials and amountsthereof recited in these examples as well as other conditions anddetails, should not be construed to unduly limit this disclosure. Unlessotherwise noted, all parts, percentages, ratios, etc. in the Examplesand the rest of the specification are by weight.

Preparation of REO-Doped Shaped Abrasive Particles with Sloping Sidewall

A sample of boehmite sol-gel was made using the following recipe:aluminum oxide monohydrate powder (1600 parts) having the tradedesignation “DISPERAL” was dispersed by high shear mixing a solutioncontaining water (2400 parts) and 70% aqueous nitric acid (72 parts) for11 minutes. The resulting sol-gel was aged for at least 1 hour beforecoating. The sol-gel was forced into production tooling havingtriangular shaped mold cavities of 28 mils depth and 110 mils on eachside. The draft angle α between the sidewall and bottom of the mold wasdifferent for each production tooling. The draft angle α was 90 degreesfor the first tooling, 98 degrees for the second tooling, 120 degreesfor the third tooling and 135 degrees for the last tooling. The 98degree draft angle production tooling was manufactured to have 50% ofthe mold cavities with 8 parallel ridges rising from the bottom surfacesof the cavities that intersected with one side of the triangle at a 90degree angle and the remaining cavities had a smooth bottom moldsurface. The parallel ridges were spaced every 0.277 mm and the crosssection of the ridges was a triangle shape having a height of 0.0127 mmand a 45 degree angle between the sides of each ridge at the tip asdescribed in patent application attorney docket number 664792US002referred to above. The sol-gel was forced into the cavities with a puttyknife so that the openings of the production tooling were completelyfilled. A mold release agent, 1% peanut oil in methanol was used to coatthe production tooling with about 0.5 mg/in² of peanut oil applied tothe production tooling. The excess methanol was removed by placingsheets of the production tooling in an air convection oven for 5 minutesat 45 degrees C. The sol-gel coated production tooling was placed in anair convection oven at 45 degrees C. for at least 45 minutes to dry. Theprecursor shaped abrasive particles were removed from the productiontooling by passing it over an ultrasonic horn. The precursor shapedabrasive particles were calcined at approximately 650 degrees Celsiusand then saturated with a mixed nitrate solution of the followingconcentration (reported as oxides): 1.8% each of MgO, Y₂O₃, Nd₂O₃ andLa₂O₃. The excess nitrate solution was removed and the saturatedprecursor shaped abrasive particles with openings were allowed to dryafter which the particles were again calcined at 650 degrees Celsius andsintered at approximately 1400 degrees Celsius. Both the calcining andsintering was performed using rotary tube kilns.

After making the shaped abrasive particles with sloping sidewalls havingthe four different draft angles, coated abrasive discs were made. Theshaped abrasive particles with sloping sidewalls were electrostaticcoated onto a 7 inch diameter fiber disc with a ⅞ inch center hole usingphenolic make coat and size coat resins as shown in Table 1. Thephenolic resin can be made from resole phenol-formaldehyde resin, a1.5:1 to 2.1:1 (phenol:formaldehyde) condensate catalyzed by 1 to 5%potassium hydroxide.

TABLE 1 Make and Size Coat Formulation Ingredient Make Coat Size CoatPhenolic Resin 49.15% 29.42% Water 10.19% 18.12% Calcium Carbonate40.56%  0.0% Cryolite  0.0% 50.65% Emulon A (BASF)  0.10%  1.81% 100.0%100.0%

The grinding performance of the shaped abrasive particles with a slopingsidewall was evaluated by grinding 1045 medium carbon steel using thefollowing procedure. 7-inch (17.8 cm) diameter abrasive discs forevaluation were attached to a rotary grinder fitted with a 7-inch (17.8cm) ribbed disc pad face plate (“80514 Extra Hard Red” obtained from 3MCompany, St. Paul, Minn.). The grinder was then activated and urgedagainst an end face of a 0.75×0.75 in (1.9×1.9 cm) pre-weighed 1045steel bar under a load of 12 lb (5.4 kg). The resulting rotational speedof the grinder under this load and against this workpiece was 5000 rpm.The workpiece was abraded under these conditions for a total of fifty(50) 10-second grinding intervals (passes). Following each 10-secondinterval, the workpiece was allowed to cool to room temperature andweighed to determine the cut of the abrasive operation. Test resultswere reported as the incremental cut for each interval and the total cutremoved. If desired, the testing can be automated using suitableequipment.

Referring to FIGS. 6 and 7, the Cut Rate versus Time and the Total Cutversus Time are plotted. As seen, shaped abrasive particles having asloping sidewall with a draft angle greater than 90 degreessignificantly out performed similarly shaped abrasive particles having a90 degree draft angle. As the draft angle approached 135 degrees, theperformance of the shaped abrasive particles with a sloping sidewallbegin to rapidly deteriorate. When shaped abrasive particles having a135 degree draft angle are compared to the shaped abrasive particleshaving a draft angle of 98 degrees, the initial cut rate was similar butthe total cut was significantly reduced. The shaped abrasive particleshaving a draft angle of 120 degrees had approximately a 20% improvementin initial cut and approximately the same total cut as blend of shapedabrasive particles having a 98 degree draft angle (grooves and nogrooves), which was unexpected. Even more surprising, shaped abrasiveparticles having only an 8 degree change in draft angle from 90 degreesto 98 degrees had a huge jump in performance. The initial cut rate wasalmost doubled and the cut rate remained relatively constant during theentire test duration. It is believed that the more consistent cut rateis a result of using a blend of 50% shaped abrasive particles withgrooves and 50% shaped abrasive particles without grooves as discussedin pending patent application attorney docket number 664792US002referred to above.

Other modifications and variations to the present disclosure may bepracticed by those of ordinary skill in the art, without departing fromthe spirit and scope of the present disclosure, which is moreparticularly set forth in the appended claims. It is understood thataspects of the various embodiments may be interchanged in whole or partor combined with other aspects of the various embodiments. All citedreferences, patents, or patent applications in the above application forLetters Patent are herein incorporated by reference in their entirety ina consistent manner. In the event of inconsistencies or contradictionsbetween portions of the incorporated references and this application,the information in the preceding description shall control. Thepreceding description, given in order to enable one of ordinary skill inthe art to practice the claimed disclosure, is not to be construed aslimiting the scope of the disclosure, which is defined by the claims andall equivalents thereto.

1. Abrasive particles comprising: shaped abrasive particles without abinder each having a sloping sidewall, each of the shaped abrasiveparticles comprising alpha alumina and having a first face and a secondface separated by a thickness, t, the shaped abrasive particles furthercomprising either: a draft angle α between the second face and thesloping sidewall, and the draft angle α is between about 95 degrees toabout 130 degrees, or the sloping sidewall having a radius, R, betweenthe first face and the second face and the radius, R, is between about0.5 to about 2 times the thickness t.
 2. The abrasive particles of claim1 wherein a perimeter of the first face and the second face comprises asubstantially triangular shape.
 3. The abrasive particles of claim 2wherein the draft angle α is between about 95 degrees to about 120degrees.
 4. The abrasive particles of claim 2 wherein the draft angle αis between about 95 degrees to about 110 degrees.
 5. The abrasiveparticles of claim 3 or 4 wherein the substantially triangular shapecomprises an equilateral triangle.
 6. The abrasive particles of claim 5comprising a first sloping sidewall having a first draft angle, a secondsloping sidewall having a second draft angle, and a third slopingsidewall having a third draft angle, and wherein the first draft angle,the second draft angle, and the third draft angle are equal.
 7. Theabrasive particles of claim 1 comprising a first sloping sidewall havinga first draft angle and a second sloping sidewall having a second draftangle, and wherein the first draft angle is a different value than thesecond draft angle.
 8. The abrasive particles of claim 1 comprising afirst sloping sidewall having a first draft angle, a second slopingsidewall having a second draft angle, and a third sloping sidewallhaving a third draft angle, and wherein the first draft angle, and thesecond draft angle, and the third draft angle are different values fromeach other.
 9. The abrasive particles of claim 7 or 8 wherein aperimeter of the first face and the second face comprises asubstantially triangular shape.
 10. The abrasive particles of claim 9wherein the substantially triangular shape comprises an equilateraltriangle.
 11. The abrasive particles of claim 1 comprising a volumetricaspect ratio and the volumetric aspect ratio is greater than about 1.15.12. The abrasive particles of claim 2 comprising an average tip radiusand the average tip radius is less than 75 microns.
 13. The abrasiveparticles of claim 2 or 12 comprising a uniformly planar slopingsidewall.
 14. The abrasive particles of claim 13 wherein the draft anglea is between about 95 degrees to about 100 degrees.
 15. The abrasiveparticles of claim 1 comprising a binder forming an abrasive articleselected from the group consisting of bonded abrasive articles, coatedabrasive articles, nonwoven abrasive articles, and abrasive brushes. 16.A coated abrasive article comprising the abrasive particles of claim 1and a make coat on a first major surface of a backing and a majority ofthe shaped abrasive particles adhered to the make coat by the slopingsidewall and having an orientation angle β between about 50 degrees toabout 85 degrees, the shaped abrasive particles forming an abrasivelayer, the abrasive layer coated with a size coat, and wherein theabrasive layer comprises at least 5 percent by weight of the shapedabrasive particles.
 17. The coated abrasive article of claim 16 whereinthe abrasive layer is an open coat abrasive layer and a percent openarea in the abrasive layer is between about 10% to about 90%.
 18. Thecoated abrasive article of claim 17 wherein the orientation angle β isbetween about 60 degrees to about 85 degrees.
 19. The coated abrasivearticle of claim 17 wherein the orientation angle β is between about 70degrees to about 85 degrees.
 20. The coated abrasive article of claim 19wherein the abrasive layer comprises at least 50% by weight of theshaped abrasive particles.
 21. A method of making the abrasive particlesof claim 1 comprising: providing a mold having a plurality of cavities,the plurality of cavities comprising polymeric surfaces; filling theplurality of cavities with a sol-gel, the sol-gel comprising particlesthat can be converted into alpha alumina in a liquid, the liquidcomprising a volatile component; removing at least a portion of thevolatile component from the sol-gel while the sol-gel resides in theplurality of cavities thereby forming a plurality of precursor shapedabrasive particles each having a sloping sidewall; and sintering theplurality of precursor shaped abrasive particles each having the slopingsidewall.